Solar critic used flawed math

To the editor:

Mr. Ross Wilkinson’s recent letter to the editor on Peterborough’s waste treatment solar project inaccurately reports its power output as a result of flawed methodology and mixing of terms and their meanings.

The writer confuses a PV system’s size with its ability to produce electricity — time must be added as a variable to understand how much electricity a system like this will produce. The correct approach to determine a PV system’s output is to start with the type and quantity of modules used. This project will use 3,266-300 Watt modules for a total DC capacity of 979,800 watts. They will face (azimuth) true south and have a tilt of 20 degrees. The “PVWatts” calculator shows (that with the .770 DC to AC derate that was correctly referenced in the letter) that the system will produce 1,166,736 kwh or 1166 mwh of electricity annually. It also shows that the array should receive an average of 4.46 hours of solar radiation (kWh/m2/day) every day of the year — the PVWatts site bases its results on many years of National Weather Service observation data that also factors in cloudy and snowy days (and night time) when the array will make less electricity.

Greg Blake


South Pack Solar

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